Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $32.84   8.664%   $35.6853   $35.69   $35.70   $35.70  
  Purchase #2 $242.25   9.537%   $265.3534   $265.35   $265.35   $265.40  
  Purchase #3 $103.82   10.249%   $114.4605   $114.46   $114.45   $114.50  
  Purchase #4 $83.71   10.792%   $92.744   $92.74   $92.75   $92.70  
  Purchase #5 $152.94   7.786%   $164.8479   $164.85   $164.85   $164.80  
  Purchase #6 $218.97   4.308%   $228.4032   $228.40   $228.40   $228.40  
  Purchase #7 $155.76   6.616%   $166.0651   $166.07   $166.05   $166.10  
  7 purchase totals = $990.29       $1,067.5594   $1,067.56   $1,067.55   $1,067.60